The invention is directed to a two-roll machine, in particular a roll press, as well as to a method for operating the two-roll machine for the pressure treatment of granular goods, with two rolls that are rotatably mounted in a machine frame so as to be able to be rotated in directions opposed to one another, separated from one another by a roll gap, between which the granular material is drawn and is subjected to interparticle pressure treatment and is thereby disintegrated. One of the two rolls can be a fixed roll whose bearings are supported on the machine frame, and the other roll can be a loose roll, supported on the machine frame by a force acting from the outside.
High-pressure roll presses or, roll presses, are known for what is called the interparticle crushing of granular material, such as for example cement klinkers, which granular materials are pressed in the roll gap at high pressure to form plate-like agglomerates, which agglomerates are subsequently disagglomerated, whereby the material, pressed once, already comprises a high portion of the desired fineness.
In known high-pressure roll presses, one of the two rolls is fashioned as a fixed roll, supported against the machine frame via its bearings, while the other roll, as a loose roll, is supported via its bearings against an external force, for example against the hydraulic cylinder of a hydropneumatic system, with which the roll pressure force is applied and the adjustment of the width of the roll gap is carried out.
In known roll presses, normally both rolls are driven in opposite directions at the same RPM, by means of separate, equally large, drive motors with the necessary components of gearing, coupling, and torque bearings.
Due to the forcible coupling of the two rolls via the granular material located in the roll gap during the pressing, a differential loading of the individual drives cannot be excluded, particularly when the two rolls differ in diameter from one another.
In addition, the coupling of the two rolls via the pressed material, with simultaneous separate driving of the two rolls, results in increased wear on the roll surfaces because the driving of the rolls forces a slippage of the speed of the pressed material in relation to the speed of the circumference of the rolls.
In order to avoid these disadvantages, in DE-38 34 425 A1 it is proposed to provide only one of the two rolls with a rotational drive, while the other roll is frictionally driven as a drag roll via the material located in the roll gap. By means of this measure, in addition to a savings of energy, significant improvements are also achieved with respect to the wearing of the roll surfaces, since the speed of the circumference of the drag roll can adapt itself completely to the pressed material. A different diameter of the two rolls is also no longer significant in this case, since an approximately equal circumferential speed arises for both rolls due to the frictional force. However, in certain operational situations there may be difficulties in starting the dragged roll, whereby disturbances in the operation are caused, in particular during the final grinding in the circulation with further systems parts (ball mill, sifter).